This invention relates to novel polymers prepared from ethylene glycol, polyethylene oxide and terephthalic acid. When applied to fabrics from an aqueous rinse bath having a pH of 3 to 10, or from an aqueous laundering solution, said polymers impart superior soil release benefits, particularly to fabrics composed of polyester fibers.
Much effort has been expended in designing various compounds capable of conferring soil release properties to fabrics woven from polyester fibers. These fabrics are mostly co-polymers of ethylene glycol and terephthalic acid, and are sold under a number of tradenames, e.g., Dacron, Fortrel, Kodel and Blue C Polyester. The hydrophobic character of polyester fabrics makes their laundering (particularly as regards oily soil and oil stains) difficult, principally due to the inherent low wettability of the polyester fibers. Since the inherent character of the fiber itself is hydrophobic, or oleophilic, once an oily soil or oily stain is deposited on the fabric it tends to be "attached" to the surface of the fiber. As a result, the oily soil or stain is difficult to remove in an aqueous laundering process.
When hydrophilic fabrics such as cotton are soiled by oily stains or oily soil, it is well-recognized that the oil is much more easily removed than in the case of hydrophobic polyester fabrics. The difference in oil removal characteristics is apparently caused by a greater affinity of cotton fabrics for water. The differences in hydrophilic/hydrophobic characteristics of cotton and polyester are due in part to the basic building blocks of the fibers themselves. That is, since polyester fibers are copolymers of terephthalic acid and ethylene glycol, they have less affinity for water because there are fewer free hydrophilic groups, e.g., hydroxyl or carboxyl groups, where hydrogen bonding can occur. With cotton, which is a cellulose material, the large number of hydrophilic groups provides compatibility with, and affinity for, water.
From a detergency standpoint, the most important difference between hydrophobic fabrics and hydrophilic fabrics is the tendency for oily soil to form easily removable droplets when present on a hydrophilic fabric and in contact with water. Mechanical action of washing and the action of synthetic detergents and builders normally used in the washing step of the laundering process removes such oil droplets from the fabric. This droplet formation is in contrast to the situation which exists with a polyester (hydrophobic) fiber. Water does not "wick" well through hydrophobic fabrics and the oily soil or stain tends to be retained throughout the fabric, both because of the inherent hydrophobic character of the fabric and the lack of affinity of oily soils for water.
Since polyester and polyester-blend fabrics (e.g., polyester-cotton blends) are susceptible to oily staining, and, once stained, are difficult to clean in an aqueous laundry bath, manufacturers of polyester fibers and fabrics have sought to increase the hydrophilic character of the polyester to provide ease of laundering.
A number of approaches to the problem of increasing the hydrophilic character of polyester fabrics and fabric blends have been taken. Many of these approaches involve a process applied by the textile/fiber manufacturer or the textile manufacturer. Netherlands Application 65/09456 [see also D. A. Garrett and P. N. Hartley, J. Soc. Dyers and Colourists, 82, 7, 252-7 (1967) and Chem. Eng. News, 44, 42-43 (Oct. 17, 1966)] describes the treatment of polyester fabrics in which a copolymer of terephthalic acid with a polyethylene glycol is padded on the polyester fiber using an emulsion containing a 20% concentration of the padding agent, a polyester swelling agent such as benzyl alcohol, and heat. The object of this treatment is to give the basic polyester fiber more hydrophilic character, thereby reducing the tendency of the polyester fiber to retain oily stains.
Different polyester fabric finishing techniques are, for example, described in: German Pat. No. 1,194,363; Netherlands Application No. 65/02428; Belgium Pat. No. 641,882; and French Pat. No. 1,394,401.
British Pat. No. 1,088,984 relates to a modifying treatment for polyester fibers whereby a polyethylene terephthalate polymer is applied to the surface of said fibers. The polymers employed contain ethylene terephthalate and polyethylene oxide terephthalate units at a molar ratio from 1:1 to 8:1. The polyethylene oxide used for preparing these polymers has a molecular weight in the range of 300 to 6,000, preferably from 1,000 to 4,000.
British Pat. No. 1,175,207 discloses a process for treating filaments and fibers by contacting same with polyesters containing from about 10% to about 50% by weight of crystalline polyester segments which are identical with the repeat units forming the crystalline segment of the polyester fiber, and from about 90% to about 50% by weight of water solvatable polyoxyalkylene ester segments. The polymers employed are identical to those disclosed in British Pat. No. 1,088,984 discussed above.
British Pat. No. 1,092,435 deals with a stable dispersion of water-insoluble graft polymers containing polyoxyethylene glycol and polyethylene terephthalate. This polymer has a ratio of ethylene terephthalate to polyoxyethylene terephthalate from about 2:1 to about 6:1. Also, the teachings of British Pat. No. 1,119,367, and Dutch Pat. Application No. 66/14134, relate to the application to fibers of surface modifying agents as described in the patents referred to hereinabove.
U.S. Pat. No. 3,712,873, Zenk, discloses the use of polyester polymers in combination with quaternary ammonium salts as fabric treatment compositions. Terpolymers having a molecular weight in the range from 1,000 to 100,000, and a molar ratio of terephthalic acid:polyglycol: glycol from 4.5:3.5:1 are disclosed. Co-pending application U.S. Ser. No. 328,824, filed Feb. 1, 1973, Basadur, relates to compositions and processes for imparting a renewable soil release finish to polyester-containing fabrics. Polyesters based on terephthalic acid, ethylene glycol and polyethylene oxide and their use in acidic fabric rinses are disclosed. The polymers have a molecular weight in the range from 1,000 to 100,000, and the polyethylene oxide link has a molecular weight of 1300 to 1800.
The concurrently filed U.S. patent application Ser. No. 482,948, inventor, Charles H. Nicol, entitled LIQUID DETERGENT COMPOSITIONS HAVING SOIL RELEASE PROPERTIES, discloses compositions comprising nonionic surfactants, ethanolamine-neutralized anionic surfactants, free ethanolamine and a soil-release polymer which can be identical to the novel polymers claimed herein.
The prior art polymers do not provide an optimum solution to the soil release problem inherent with any hydrophobic fiber mainly because of lack of durability and marginal-to-unsatisfactory soil release performance. Moreover, many of the prior art soil release polymers lack the necessary substantivity to fibers under conditions of neutral-to-alkaline pH, i.e., under common laundering conditions. In addition, some of the known polymers seem to require calcium ions for fiber substantivity. Of course, the presence of free calcium or other water hardness cations is preferably avoided in a laundering operation.
It has now been found that certain hydrophilic terephthalate-based polymers having critical ratios of monomer units as well as critical limitations on the molecular weight of the hydrophilic moieties in the polymers are particularly useful as soil-release agents. The in-use superiority of the polymers herein over those of the prior art is surprising in that nothing in the vast literature in this area suggests that the critical polymer design now provided would have any additional effect on soil release properties.
It is the object of this invention to provide novel soil-release polymers based on ethylene terephthalate and polyethylene oxide terephthalate.
It is another object of this invention to provide a process for imparting an improved soil release finish to hydrophobic textiles, especially polyester.
The above objects are met through the discovery of novel terephthalate polymers which are unexpectedly valuable for the surface treatment of textiles.